Survey of New Solar Results

Abstract

Following a brief historical review, new observations of the sun in the wavelength range 3000 to 20 Å are surveyed for the period since about 1958. Vehicles employed have been sounding rockets, the OSO (Orbiting Solar Observatories), balloons for the window 2300–1900 Å and for λ > 2700 Å, and small orbiting observatories such as Solrad, for XUV solar monitoring. Advances have been made in spectral resolution, using echelle gratings and also Fabry-Pérot interferometers. Much progress has been made towards increased spatial resolution, to obtain spectra of specific solar features and to analyse the chromosphere and corona. Methods employed include spectrographs that are stigmatic, or that have a stabilized solar image projected onto the slit; slitless objective-type spectrographs; and observations during a total eclipse. Spectra have been obtained of a solar flare, showing its form and intensity in the emission lines between 171 and 630 Å. From OSO 4–6 many XUV spectroheliograms and spectra have been obtained over the range 300 to 1350 Å, with spatial resolution 35 × 35 arc sec in OSO 6. Photographic XUV spectroheliograms have provided solar images with spatial resolution as great as 3 arc sec in some cases. Although much effort has been spent to increase the accuracy of XUV intensity measurements, a great deal remains to be done before the requirements of solar physics theory are satisfied. Line identification, however, is proceeding well, although more laboratory spectroscopy is needed. Not included in the survey is the Bragg Spectrometer X-ray range below about 20 Å.